[time-nuts] Where does 28V come from?

Magnus Danielson magnus at rubidium.dyndns.org
Tue Jul 21 20:35:43 UTC 2009


Dave,

dave powis wrote:
> Phone companies work off a standard 48v (often referred to as 50v) for exchanges and 'in building' installations.  This includes mobile phone operators.  But a significant amount of equipment in the mobile network is not in the exchange sites - it is in the BTS (Base Transmitter System) cabinets, where 28v is used.  Henace a lot of ex-mobile phone co equipment, such the HP/Symmetricom Z380xx, Lucent RFTG's that were around, and power amplifiers used on 23 and 13cm amateur bands, is normally capable of being powered from either 28V or 48V supplies, since it could be deployed in either situation.

In all environments I encounter it, it is called 48V and not 50V. There 
also exists a -60 VDC standard. For Europe, it is standardized as ETSI 
EN 300 132-2. For US Bellcore (now Telecordia) wrote it into it's NEBS 
series, but I can't recall the number from the top of my head.

The ETSI variant is online, so fetch that.

The ETSI people have created another interesting spec, the EN 300 132-3 
which is for a 400 VDC system. It avoids the step of DC-AC conversion in 
  UPS systems since most supplies rectifies it anyway. Check it out. :)

Cheers,
Magnus



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